INTRODUCTION
Heading through this autumn, we’ve heard the usual scramble of noise is ongoing from social media pages – nothing unexpected, and this is not my space set aside to editorialize about all of that. This is to talk about my thoughts on the upcoming winter after carefully considering all of the factors that go into influencing and shaping the large scale weather pattern over a period of nearly 4 months. No easy task, but a fun undertaking nonetheless. You’ve heard the early hype about Sudden Stratospheric Warming and Polar Vortex disruption, a big start to winter, etc., etc. – but it’s time to set that aside and start from the beginning, and progress through each potential driver, then put it all together in a science-driven “best-guess”.
OVERVIEW
Last year heading into winter we were sitting at ENSO-neutral heading for a weak La Nina. This year, it’s opposite. Of late, ENSO has been right on the border of weak La Nina and neutral. I mentioned last year about a string of winter where MJO did not play favorites for snow-lovers, and we waited to see if it would become more favorable for events that would make the chionophiles happy – but it didn’t really rise to the occasion. So once again we wait to see if it finally decides to be more giving this upcoming winter. That said, as you know, there are many more factors that can and do influence the large scale patterns that ultimately determine the character of the winter season. If you have forgotten what ENSO / La Nina / MJO mean, don’t worry. I’ll be making all of that clear along with all of the other indices to be talked about. There are two other factors this year that are somewhat similar to last year heading toward winter. Those are the lingering impact from the Hunga Tonga volcano with still quite an elevated water vapor level in the stratosphere, as well as the region having been at least borderline in drought for a good portion of the summer and part of autumn. One general weather rule of thumb, as I mentioned in last year’s outlook when talking about this, is a wet autumn often leads to at least a somewhat wet (potentially snowy) winter. But again, as of now we are still not seeing that wet an autumn pattern with most of the region having precipitation totals that fall shy of the long term average. So there you go. Let’s move on and systematically break down all the contributing factors to the pattern that will be winter 2025-2026, and then put it all back together into an outlook for the season!
MAJOR INDICES / IMPACTS
Hunga Tonga Volcanic Eruption, January 2022 (HTE): We continue to observe and learn about the impact from the tremendous influx of moisture into our stratosphere, and the idea remains that climate influence from this event will be around for at least a few to several more years, with results becoming more clear with time. So for this winter, it remains as a wild card player that cannot just be “under rug swept”, to borrow an Alanis Morissette album title from 2002.
El Nino Southern Oscillation (ENSO): This index is pretty straightforward this time. While sitting on the neutral / weak La Nina border of late, a movement back into weak La Nina is nearly certain as we finish November and move into December. As we progress through the winter, the expectations are to come back to the neutral phase where it will remain for the finish of the season. I’m currently expecting about 1/2 the winter in weak La Nina and the other half neutral. History shows some of our snowier winters have occurred in weak La Nina and neutral conditions. However, as I’ve said many times, one index does not determine the conditions on its own.
Arctic Oscillation (AO): This is the index that indicates the strength and behavior of the Polar Vortex (PV). To review quickly, a positive AO indicates a strong PV, fairly tight to the polar regions with limited southern movement and tends to promote seasonable to mild air at mid latitudes with fewer sharp changes, while a negative phase indicates an interrupted or unstable PV with lobes of it gaining the ability to drop to much lower latitudes. These bring your colder outbreaks of air to mid latitudes, the duration and location determined by the behavior of the PV lobe of cause. Going into this winter, we’re already experiencing a well-forecast disruption of the PV. It currently remains to be seen precisely the magnitude and duration of the interruption, which results in a negative AO. The strongest indications are that it will have staying power at least through the first half of December, and possibly through much of the month. This increases the opportunity for colder bouts of air to visit North America, including our region. But the details – timing, number of cold shots, duration of cold shots, all remains to be seen. The next index talked about below does have an influence on this. Look ahead to read about that and what it might mean for the AO beyond December.
Quasi-Biennial Oscillation (QBO), the direction of stratospheric winds above the tropical latitudes: This index is expected to be in its negative phase, otherwise known as an easterly QBO, for the duration of this winter. A QBO in this phase increases the chances that the PV can be disrupted and the AO can go negative. While I’m pretty certain, as noted above, this is how winter starts, based on the forecast QBO remaining easterly, this leaves the door open for additional negative AO episodes going through winter, which would favor the tendency for colder over warmer.
North Atlantic Oscillation (NAO): In its positive phase, this index describes general low pressure north and high pressure south in the North Atlantic Ocean, and the pattern in this phase also is a fairly progressive jet stream pattern, often blowing across Canada and/or the northern US and into North Atlantic without being hindered along their path. In its negative phase, high pressure is more dominant in the north, with low pressure to the south. This describes a blocking pattern, which with high pressure sitting over the North Atlantic, Greenland, or Atlantic Canada, forces the jet stream to the south. This tends to be associated with colder and/or stormier weather in the US Northeast. However, this can be a dry pattern if the blocking is too strong or oriented in such a way that the high pressure area is too far west. Predicting this index becomes highly uncertain beyond a couple weeks. Last winter there was no strong indication one way or another for this index heading into winter. This year, this index spent most of the autumn in negative territory, but recently trended neutral to slightly positive as we lost a Greenland blocking pattern. As we enter the first part of meteorological winter, the outlooks are for this index wavering around neutral – slightly positive to slightly negative. This isn’t unusual for the type of pattern transition ongoing now. There is not really way to forecast this index beyond a couple weeks with any real skill. What I can say is that in a winter where there is the opportunity for episodes of -AO, there can be more opportunities for -NAO episodes that bring your higher chance of cold and sometimes stormy weather. This is something we’ll have to monitor as time goes along.
Pacific Decadal Oscillation (PDO): a water temperature pattern in the mid latitude Pacific Ocean, north of 20 degrees N latitude. Just like last year, the PDO remains strongly negative. The primary result of a strongly negative phase of this index is coldest weather (relative to normal) often occurs from the Pacific Northwest to the Upper Midwest, and warmest (relative to normal) occurs in the South Central US, Southeast, and at times the Mid Atlantic. The negative PDO often promotes more low pressure trough occurrences in the West, with downstream ridging and corresponding milder weather to the east – with focus often Deep South to Southeast / Mid Atlantic – depending on the status of other indices of course. With La Nina present at least for the early part of winter, this is something we may see occur as would be expected. A shift to a neutral ENSO may dampen this effect somewhat.
Pacific-North American Index (PNA), which describes the upper air pattern from the North Pacific into North America): When this index is positive, it’s associated with high pressure ridging in the western portion of North America and a tendency for low pressure troughing in the eastern portion of North America. This index pulled a fast one on me last year, going weak to moderate positive when I was anticipating weak to moderate negative. This index can be and often is influenced by ENSO, with negative phases associated with La Nina episodes and positive phases associated with El Nino episodes. This index has spent much of the autumn in a positive phase, but recently has trended more to neutral territory. Indications to me, including our tendency to see our La Nina fade to neutral with time, are that this index will remain close to neutral for a good amount of time this winter, with no strong notable impact on the large scale pattern.
Eastern Pacific Oscillation (EPO), which is similar to NAO, but in the eastern North Pacific: A positive EPO is a mostly zonal or lower amplitude pattern which allows mild Pacific air into the US more readily, while a negative EPO features more high pressure ridging in the northeastern Pacific and Alaska, blocking Pacific air, and driving colder air southward out of Canada into the US, the longitude of the coldest determined at least in part by the placement of high pressure and downstream troughing. Heading into this winter, the strongest indications are for the EPO to want to be in its positive phase. This would leave the door open for more Pacific air to enter the US via the West Coast. What happens from there would be dependent on the status of other indices. One potential is that this index contributes to milder spells for the Northeast especially when low pressure areas find their easiest pathway to be through the Great Lakes if we have the presence of a stronger Southeast Ridge, and the NAO is in its positive phase.
Indian Ocean Dipole (IOD), an index that measures water temperature tendencies in the Indian Ocean, and found to have some impact on the large scale climate pattern: A positive IOD features warmer water and increased convective activity in the western Indian Ocean and nearby land masses while cooler water dominates the eastern Indian Ocean with less convective activity and resultant rainfall for southeastern Asia as well as Australia. This phase has been correlated to a stronger PV in the northern hemisphere. A negative IOD produces the opposite – cooler water in the western waters, warmer waters to the east with more convective activity and rain in southeastern Asia / Australia, and a weaker PV in the northern hemisphere. The IOD is again, similar to last winter, anticipated to be neutral this winter, and not a considerable factor of influence.
Madden-Julian Oscillation (MJO), which describes convective focus in equatorial regions and has 8 phases depending on the location of the normally eastward-drifting convective wave: It’s known that the Northeast has a better shot at snow / wintry weather with MJO in phases 7, 8, and 1 early in the season and in phases 8, 1, and 2 as the winter progresses. The MJO has been the “enemy” of the snow lover many times in southern New England during the last several winters. While some recent signs point toward this index being more of a factor heading into this winter, there is not a 100% certainty as of yet. Previously, a more prominent incarnation of this index found it sitting in phase 6, with promise (if you’re a snow lover) that it’s set to migrate into the early season favorite phases for snowfall as we enter December. But not so fast. There is some pretty solid consensus that this index will make it into phase 7 as we head out of November and into December. And additional indication – though less certain – that it heads toward phase 8 as we near mid December. But there have also been increasing indications recently that the MJO will also display a weakening trend, lessening its overall impact with time. So far, I don’t think it trends to “non-factor” status, but it may end up more as a “muted-factor” index at least for the early part of the winter. If this index follows its typical progression, it will eventually find its way into phases 1 and 2 during mid winter and probably to less favorable places, again from a snow-lover’s perspective, later in the winter. But the wild card remains – how much of a factor will it turn out to be? Time will tell, but for now I’m tempted to put a little less emphasis on this index as a major influence lasting through the winter.
Solar Cycle: This cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a periodic (about 11 year) change in solar activity as measured by solar storms, or sunspots, on the sun’s surface. There has been a correlation observed that high periods of solar activity tend to correspond to milder winters overall, but this is not a solid correlation and more or a base guideline. A more useful aspect of the ability to measure this is to tell when we may see greater or fewer episodes of the aurora, and the potential for disruptions of satellite communication. Solar Cycle 25, which peaked this past July, has been a giver in terms of aurora displays, with another recent solar storm providing a spectacle on the evening of November 11. While the cycle is past peak, it remains high for winter 2025-2026, but its impact on the winter – i.e., milder influence – may be muted by other factors, which was most certainly the case last year as well.
So there you have it – a look at the major indices that have potential to influence our large scale pattern and resultant weather events for winter-upcoming! As always, I must remind you that even knowing all of this, there is still a significant degree of uncertainty and resultant unpredictability with longer range forecasting. As always, it will be interesting to see what kind of surprises may await that contribute to the conditions defying some of the expectations. It’ll take us all winter to discover it!
So I’m going to do something a little different here, and list from “most influencial” to “least influencial” the indices in terms of how they will impact our winter: 1. AO 2. ENSO 3. QBO 4. NAO 5. MJO 6. HTE 7. PDO 8. EPO 9. PNA 10. SS25 11. IOD
DISCUSSION SUMMARY
It seems like “variability” has been the word of the last few winters, and never has it been as true as how I feel about going into this one. Yes, every season is going to have variability as it’s the nature of our weather anyway. But it looks like the contrasts may be a little more pronounced than usual this go-around. I’m going to paraphrase myself from last year here because I feel this is an important set of points to make and should be repeated: We’re not looking at cold from start to end, warm from start to end, wet / snowy / dry from start to end. There are enough conflicting indices to know we’ll see a few battles to see which one has the greater impacts, and they may wrestle back and forth a few times, but we still should see some general trends that are easier to spot. The aim of the long range forecast is to try to identify what these longer term trends will be. It almost doesn’t matter what the sum of them ends up being, because the impacts of temperature, wind, rain/snow are most strongly felt during the events, not so much over the entire season, but on an event-by-event basis. The longer term trends are more important for things like agriculture, or heating bills. People remember the 2014-2015 winter for its incredible stretch of snow and cold from the very end of January to the very beginning of March, and nearly forget that winter was almost “non existent” up until that point. They remember the individual storms in that stretch, and the stretch itself, but over a much shorter period of time than the entire winter. And with that, it’s now time for me to go to the best possible monthly breakdown I can give you, based on everything discussed above.
DECEMBER
We enter meteorological winter with a battle between a high pressure ridge south of us – “The Southeast Ridge” and an elongated lobe of a disrupted polar vortex making some progress into the US from Canada. We’ll probably see an overall -AO but some oscillation between negative and positive. We’ll be in weak La Nina as a major factor as well as the ongoing easterly QBO. The pattern is likely to alternate between a storm track that brings low pressure areas through the Great Lakes – during +NAO periods, and more of a clipper type storm track during -NAO periods. While we can get some snow from any Great Lakes lows that redevelop just to our south if we’re NAO-negative or transitional, we may see most of whatever snowfall we end up with from the clippers, which would occur during colder spells. There’s a lot of potential volatility in this pattern, and it may seem to frantically flip from one regime to another more than a couple times. This can result in some pretty wild temperature swings, even without significant storminess impacting the region. So while I lean away from some of the “promises” of a very cold and snowy December that you probably heard out there on the internet, I don’t lean far enough away to say it’s going to be a very mild, snowless December either. The truth lies between the two. Because I think we’ll be in “clipper” mode more of the time than we’re in “cutter” mode, the leaning from me will be to slightly below normal in the temperature and precipitation for the month with the result being overall slightly below normal snowfall. Just keep in mind all it takes is one over-producing snow event to put some locations over the top of normal. White Christmas chances? Ask me about a week before the holiday. I’m not going there in this outlook! 😉
JANUARY
Anticipating the behavior and level of impact of the indices discussed above, our January displays some similarities to the December pattern. We know we’re likely to have the easterly QBO humming along, and we’ll be on the watch for a continued unstable PV leading to a leaning toward a -AO and episodic -NAO periods. The question to answer: La Nina holding on, or back to neutral ENSO? Leaning former over latter. The time we spend with -NAO vs +NAO is probably the biggest factor in the snowfall totals for this month. I think we’ll have enough cold around most of the time, unless we have a storm coincide with a +NAO and a time when the SE ridge has made too strong a return. I think that will be the exception though. A lot of variability in temperature should work out to be about the long term average for the month, and both precipitation and snowfall should exceed the long term averages due to the EPO’s contribution of more Pacific moisture to coincide with cold air in place in our neighborhood.
FEBRUARY
Last year, my forecast for February was for a strong PV and positive AO with a milder, drier month. Turns out Mother Nature decided to taunt me for trying to predict that far in advance, and much of the region was a little colder than normal and, while not crazy, it ended up as the snowiest month of the winter. Humbling, but not enough to stop me from trying. This time I’m going to rely on QBO peaking in easterly phase to dishevel the PV enough to supply fairly regular influxes of cold from Canada. One of my favorite major climate models has been adamant about a chilly February for many forecast cycles now, so I can’t say this hasn’t been an influence on me. We should see the EPO’s influence fade with less Pacific moisture available, and we may be back to a clipper-type pattern again to bring us the majority of whatever snow we get. With this being the primary source, it could end up being a drier than normal month overall. MJO is a wildcard here. If it progresses slowly enough, it may still be in a phase favorable to support snow. If not, it may be beyond the favorable phases and into unfavorable ones (3, 4, 5).
MARCH (UNTIL EQUINOX)
By this time, I expect ENSO to be neutral, AO to lean negative, NAO not determinable so a wildcard, QBO still easterly, and no major influence from other indices. Obviously, this month being furthest away from now and long range forecasting being as risky as it is, I’m not going to be highly confident, but if I had to lean in any direction that at least makes it sound like I have an idea – it’s that we’d be in for a near normal temps / near normal precip & snow kind of end to the winter. Always keep an eye out for that renegade bigger hit though, because even though the pattern doesn’t scream “biggies” this winter, you can never rule them out.
WINTER SEASON OVERALL
Temperature: Slightly below normal (departure -1F to -2F).
Precipitation: Slightly below normal (departure about -2 inches).
Snow: Near normal (departures generally within 10 inches of normal for a given location).
-Boston 45-55 inches
-Worcester 65-75 inches
-Providence 40-50 inches
-Hartford 50-60 inches